[5.3] MSTR-275: do not require sub module, let core handle it (#195)

If the app assets is loading from external `source_url`, if the app tries to require its
sub modules directly it will fail and the app won't load at all.

Changing the module name to its external `source_url` as what Monster UI core was
previously doing won't always work in case the sub modules were small enough and optimized
away in a single file as `app.js`. This has been observed with `branding` and
`call-recording` apps so far.

Instead we can explicitly config the paths for sub module and its external source url for
`requirejs` to load it, if it is not already optimized in the `app.js`.

Without this change, because `app.js` is requiring the submodules, this URL will be used
instead of external source_url:

```
http://{monster_ui_url}/apps/:appname/submodules/{submodule}/{submodule}.js
```

`requireSubModule` from `monster.apps.js` will require all submodules
defined on the app and can adds external `source_url` of the sub module in requirejs
config so the correct URL will be used for fetch if it is needed:

```
http://{app_metadata.source_url}/submodules/{submodule}/{submodule}.js
```

Read more: https://requirejs.org/docs/jquery.html#modulename

app.js

@@ -4,19 +4,13 @@ define(function(require) {
 		monster = require('monster'),
 		timezone = require('monster-timezone');
 
-	var appSubmodules = [
-		'serviceItemsListing',
-		'wizard'
-	];
-
-	require(_.map(appSubmodules, function(name) {
-		return './submodules/' + name + '/' + name;
-	}));
-
 	var app = {
 		name: 'accounts',
 
-		subModules: appSubmodules,
+		subModules: [
+			'serviceItemsListing',
+			'wizard'
+		],
 
 		css: [ 'app' ],